(EDIT: Problem solved, thank you to all who helped. This post hasgarnered some great information so if you are having problems with the laser and you cannot determine whether it’s the PSU or the tube, then read through these comments and learn something new.)
In the middle of an engraving, the laser lost all of it’s power but continued on it’s route. No power at all and the amp meter shows nothing. There’s no cracks in the tube, seems perfectly fine, but no visible beam at all. LED and fan is still working on the power supply, and there’s no signs of blown cap’s, resistors, etc on the PCB. Perhaps a MOSFET went bad? What’s the chances of that happening?
I’ve got the power supply opened up now and I don’t see anything unusual. I’m not thrilled about playing around with the anode and cathode on the tube but I’m wondering if there’s a bad connection.
Anyhow, I can post up some more pics if needed. Does anyone know where I should start with this? I don’t want to go purchasing a new tube or power supply just yet. How can I tell if the tube is bad aside from a visual inspection, because visually the tube seems fine and holding water where it should be. Worst time for this to happen, Holidays and all… please help.
Hi Joe, thank you for the reply. After making this post, I went down to tinker some more and hitting the on-board “TEST” tactile switch was one of the tests I preformed.
I was hoping it would only be a control switch issue, as that fix would be a piece of cake. But unfortunately the “TEST” switch on-board did not result in anything.
Any other suggestions? Do you know what the red slide switch is on the side of the blue box power supply?
I’m wondering if it’s some sort of relay or breaker I might have to reset but I don’t know what it is because the data sheets for that board are all in Chinese…
@Andy_Shilling yes that would make sense to me, as these lasers are distributed to many countries. As for metering the outputs, great call, perhaps I should try that first. My plan was to start testing resistors and caps, particularly the big green resistor on the ground return. I’m eyeballing those MOSFET relays too, but the only method I know of testing FET’s is quite the process. I’ll meter the outputs soon as I head back down in the shop in a few mins and report back.
@StephaneBUISSON I can see the preview on the last video which I recognize, but I’ll have to check out the first 2 and see if I’ve already watched them because I must have watched at least 15 videos so far regarding power supplies, never mind the tube videos lol… And yes, agreed, I always get a kick out of watching the Chinese assemble these things, swinging around 20,000 volts like it’s just a wire to some headphones. Can only imagine the injury statistics in those factories!
Hopefully I can help you rather than confusing…
First of all, the following steps are actions I personally would do to find the problem, so this is definitely not a recommendation, only to be clear and I hope you understand this.
Where is the main problem? You don’t have a tool to measure HighVoltage, right? I come to this point later.
What is my experience as service technican? at least 90% of all problems are of mechanical nature!
So, first of all I would check the connection from the tube to the amp and to ground -> should be very near to zero ohms. The problem zones are the tube connection, both screws on the amperemeter, the amperemeter itself and the connection to the PSU. Doblechek this with an OHM-meter (disconnected and discharged of course).
Next is to see if HighVolage is present:
I the company I worked in, we had a HV-Probe. This is a long full isolated “stick” with an output to a multimeter. Maybe you can find an old TV-repairing shop near by you, they could have such a probe and lend it to you (old TVs have comparable voltage ranges on their tubes). If not, as I know, the isolation of air is about 21KV/cm, I would do the “risky” method but in a safely way. Everything unpowered and discharged I would mount a really small wire from ground to lets say 1/2cm or some mm to the HV-connection. Then going to the frontpanel, swich on and press Test, first short, then longer, until you hear or see the spark…or you hear nothing… in this case there is with some certainty NO High voltage. I would then power OFF, and shorten the HV-connection with the wire using a long isolation stick (i.e. Wood). Again, if there is no spark it manifests the previous assumtion.
At his point you should know, on which side the problem is: on the tube side or on the PSU-side.
Maybe it helps a little bit for your decisions…
PS: if the PSU is damaged (what I believe, reading your error report) you can quickchek the MOSFETS if they are shortened (ohmmeter). They should be High-Zero (PSU unplugged and discharged of course)! https://drive.google.com/file/d/0BxRBPjkKUvRUN1Q3OTlqNFhVQkJnYW5VTjRXUWduaEp5Wnd3/view
@java_lang Thank you so much! No I do not have a HV probe but I am looking for other ways to check high voltage and see if it’s there.
I am going to try your test now and report back. I also suspect the MOSFET’s could be the issue as well. Either way, thank you. Do you know any other methods of checking for HV? My wife just offered to run to the store for packing peanuts so I can preform the “peanut test” I learned back in grade school. Styrofoam packing peanut on a thread! I plan on making a video of the test, she should be back shortly and I’m on it.
Ammeter is coming back at 3.0Ω , Java, I think you just may have saved the day. Time to get a closer look at this ammeter. You it be wise to bypass/bridge the contacts on the ammeter just to see if the circuit will complete and fire the laser? That’s what I’d like to do next if there’s no harm in doing so to the laser or PSU
Have you the PSU disassembled?
2 things are coming in mind:
If a MOSFET is damaged, I would think the fuse also would be blown.
But anyway, check if there is a short on the output of Q6 or Q5.
Another posibillity is that the output transformer has simply “lost connection”, i.e. internal a wiring has disconnected or melted. Carefully discharged, you should measure a resistance from the “hot wire” to ground (if the hot wire connection is accessable).
@java_lang Yes, PSU is currently open. I am going to check the FET’s resistance and also check the Q6/Q5 as you mentioned. When you say the fuse would be blown if the FET was bad, do you mean the in-line glass fuse on the board? Here is the current state of the laser as we speak… http://imgur.com/Q6x7Sya
I just took the tube right out, filed off some corrosion on the annode/cathode prongs and cut new splices in the wire. At least I can eliminate bad connection that way. Also, I really am anxious to preform the high voltage test but I’m trying to take advantage of the machine being off for 48+ hrs and do what I have to do now, before I fire it back up and have the cap’s and flyback all charged up again. I hate high voltage.
